It is known to provide a pneumatic tire casing with a fill to create a flat-proof assembly when fitted to a wheel of a vehicle. One common method is to fill an assembled tire and wheel with a hardening material under pressure that hardens and creates the fill. Once such material is urethane liquid accompanied by a hardening agent.
Urethane filled tires have a number of disadvantages associated therewith. Known methods of filling assembled tires and wheels often require a factory site. Urethane filled tires cannot be employed on vehicles which are to be driven at high speeds, as such results in heat build-up between the rubber tire casing and the urethane fill.
Furthermore, urethane is expensive and has limited reusability when the tire casing is worn out and discarded. Machine operators dislike the rough ride of vehicles having urethane filled tires. Further, filled tires have a high rolling resistance which contributes to the rough ride and results in high fuel consumption. Urethane filled tires are also difficult to retread and, owing to the problem of casing stretching, often loosen at the rim resulting in a loss of pressure.
Where solid vulcanized polymers other than urethane are used as tire fills, similar problems are encountered, especially reversion to liquid when used at high speeds owing to the heat generated between the casing and the fill. The polymer in liquid form can leak from a loose rim or from a cut or puncture in the tire casing. Low density foamed rubber is preferable, if it could maintain its strength at high speeds.
The best known of the presently used tire fill systems is the use of high density foam rubber as illustrated in published U.K. Patent Application No. 2,164,903A to O'Coin. As is described in this patent, independent concentric rings of high density foam rubber are manufactured and installed in pneumatic tire casings. Although this system works well, there are a number of disadvantages inherent in manufacturing and installing independent concentric rings in pneumatic tire casings. First, due to the vast number of different sizes and shapes of tires, it would be necessary for an installer to carry a huge inventory of rings. Further, the tooling required to produce the vast number of shapes and sizes of concentric rings is extremely expensive. Finally, forming the filler layers in concentric rings hinders their insertion into the pneumatic tire casing.
There are other known filled pneumatic tires, such as my previous designs schematically illustrated in FIGS. 1 and 2. My previous design tire 2 of FIG. 1 has a fill including concentric rings 10, 12 and 14 disposed on a rim 16 and inside a casing 20, shown in its rest state 21. In use, casing 20 heats up and expands to an expanded state 22, rest state 21 being shown in broken line in FIG. 2. Expanded state 22 causes a space or void 30 to develop between outermost ring 14 and casing 20 in its expanded state 22 (FIG. 2).
Additional unillustrated gaps often develop between adjacent concentric rings, and between innermost ring 10 and rim 16.
Rest state 21 of my previous design casing 20 is shown in broken line in FIG. 2. Void 30 leads to even more heat build up between outermost ring 14 and casing 16. The voids between adjacent rings, and between ring 10 and rim 16, likewise cause heat build-up and thus heat deterioration of the rings. Outermost void 30 reduces the puncture-resistance of casing 20.
Thus, there is a need in the industry for a better filled tire which enjoys the advantages of layer fills without the disadvantages thereof.